Signal-translating stage



Sept. 15, 1942. J. c; WlLSON SIGNAL-TRANSLATING STAGE Filed Sept. 9,1940 2 Sheets-Sheet l o. .m R wm am m J E... u WP M A m 4 5 f m R N m 0T T .l A o m w 0 L P m x F O a B R -c m m P VE m 2.. F

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INVENTOR 0. WILSON OHN ATTORNEY Sept. 15, 1942.

FIG. 3.

J. C. WILSON SIGNAL-TRANSLATING STAGE F IG.4

FIG. 5.

oo- -o o- -o OSCILLATOR' INTERMEDIM'E' DETECTOR AUDIO- MODULATORFREQUENCY AND AVC FREQUENCY AMPLIFIER SUPPLY AMPLIFIER -o --0 Q o- -0 Q--0 1" FIG.6.

INVENTOR OHN 0. WILSON BY ATTORNEY Patented Sept. 15, 1942SIGNAL-TRANSLATIN G STAGE John 0. Wilson, Bayaide, n.1,

aasignor to Hazeltine Corporation, a corporation oi Delaware ApplicationSeptember 9, 1940, Serial No. 355,942 9 Claims. (01. 179-171) Thisinvention relates generally to a signaltranslating stage adapted totranslate a signal input having a wide amplitude range and particularlyto such a signal-translating stage in which the direct current componentin the output circuit thereof does not vary appreciably as the gain ofthe stage is adjusted over a relatively wide range.

In some modulated-carrier signal-translating systems, the amplitude ofthe signal input to a signal-translating stage varies within very widelimits. This is true of the first signal-translating stage of amodulated-carrier wave-signal receiver under normal operatingconditions. For weak signals it is desirable to maintain thetransmission characteristic, or the response, of the preselector betweenthe antenna and the first repeater stage of the receiver at a maximum inorder to raise the received signal substantially above the noise level,thus to procure maximum useful sensitivity of the receiver. However,with a high gain in the preselector, as 'the strength of the desiredreceived signal increases to such an extent that the grid swing ofthefirst repeater stage includes a substantial nonlinear portion of thecharacteristic curve of the repeater, distortion of the desiredsignal-modulation envelope and cross modulation of the desiredsignal-carrier wave by strong undesired signals may result. This isparticularly true in the case of receivers provided with automaticamplification control by which strong signals cause the grid of thefirst repeater stage to be biased toward that portion of itscharacteristic which is most nonlinear. signals, as well as desiredsignals, which reach the grid of the first repeater stage of thereceiver have the effect of causing the grid to swing over such anamplitude range that these disturbing efl'ects result. It is well knownthat such envelope distortion and cross modulation are effects whichcannot be filtered out by succeeding selector circuits of the receiver.

In general, the preselector of a receiver should be selective to pass aband of desired modulation frequencies sufilciently wide to provide thedesired fidelity of reproduction. Generally speak n if an attempt ismade to decrease the total desired and undesired signal input of thefirst repeater stage by discriminating against the undesired signalspassed by the selector by adjusting its -band width, the fidelity ofreproduction is impaired to an undesirable degree. Further, this doesnot remove the envelope distortion of abnormally strong desired signals.

Various expedients have heretofore been protenuating the input to thefirst repeater stage of a modulated-carrier signal receiver in order toeliminate the disturbing effects described above. In certain of thesearrangements, adjustable impedanceelements, such as vacuum tubes, haveWhile such arrangements provide generally satis- Undesired factoryoperation, they have usually required the use of one or more additionalvacuum tubes, or other circuit complexities which tend to increase thecost of the receiver.

Another arrangement which has been utilized for the purpose is thatdescribed and claimed in the copending application of Arthur V.Loughren, Serial No. 335,238, filed May 15, 1940,

' now Patent No. 2,263,825, November 25, 1941, and

assigned to the same assignee as. the present application. While thearrangement of the said copending application is generally satisfactory,one characteristic of the system which is undesirable in certainapplications is that the direct current component in the output circuitof the stage varies as the gain of the stage is varied.

- This characteristic is also found in the other prior posed forautomatically and adjustably tart arrangements mentioned above.

In certain applications it is disadvantageous to utilize anadjustable-gain signal-translating stage the unidirectional component ofthe output current of which varies with the gain-of the stage. Thus, ina television video-frequency amplifier it is necessary to translatesignal components of very low frequencies. If such a signal-translatingstage having an adjustable gain is utilized in a television transmitter,any gain adjustment which is effected upon the stage usually has theeilfect of temporarily interrupting or adding spurious transients to thepicture transmission for an appreciable interval, due to the timeconstants of the circuits utilized in the coupling system of thevideo-frequency amplifier. Such interruptions and spurious transientsare highly undesirable and it is, therefore, desirable to provide asignaltranslating stage the gain of which may be adjusted within widelimits and the unidirectional component of the output current of whichis not subject to an appreciable variation with the ain adjustment.

Also in preattenuator circuits of the types described above, the directcurrent component of the adjustable-gain stage used in such stagesvaries widely with an adjustment of gain oi? the signal-translatingstage, as described above. This is particularly true of adjustable-gainsignal-translating stages utilizing a variable-mu tube of conventionaltype. The range of variation of the direct current component of suchstages may be more than :1 and such a wide range of variation may tendto affect appreciably the voltage regulation of the supply source. Itis, therefore, highlydesirable to provide an adjustable-gainsignal-translating stage the gain of which may be varied over widelimits and the output current of which is substantially constant underany conditions of gain control.

It is an object of the present invention, therefore, to provide animproved signabtranslating stage which is not subject to one or more ofthe above-mentioned disadvantages of prior art arrangements.

It is a further object of the invention to provide an improvedsignal-translating stage the gain of which is adjustable over a widerange of values- It is still another object of the invention to providea signal-translating stage the gain of' which is adjustable over a. widerange of values and the direct current output of which does not varyappreciably with adjustments of the gain of the signal-translatingstage.

In accordance with the invention, a signaltranslating stage comprises apair of signal-input terminals and a vacuum tube, including means forforming an electron beam the crosssection of which is limited in atleast one dimension, and a control grid intersecting the electron beamand wide relative to the width of the beam in the limited dimension. Thestage further includes means for coupling the control grid between theinput terminals efiectively to comprise a voltage divider across itswidth and means for deflecting the electron beam in the direction of itslimited dimension to control the gain of the stage by the action of thecontrol grid.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the accompanying drawings, Fig. 1 is a schematic circuit diagram of acomplete television transmitting system including a signaltranslatingstage in accordance with the invention; Figs. 2, 3, 4, and 5 illustratedetails of the tube of the signal-translating stage of Fig. 1incorporating the invention; while Fig. 6 is a circuit diagram, partlyschematic, of a complete television receiving system embodying asignaltranslating stage in accordance with the invention as the firststage in the signal-translating channel of the receiver.

Referring now more particularly to Fig. 1 of the drawings, there isshown a schematic circuit diagram of a, television transmitting systemcomprising a video-frequency signal generator ll, which may include theusual cathoderay signal-generating tube and scanning and wave-shapingapparatus. Connected in cascade to the output circuit of the signalgenerator I3,

in the order named, are a first video-frequency amplifier II, a secondvideo-frequency amplifier l2, a third video-frequency amplifier IS, amodulator I4 and an associated carrier-frequency oscillator l5, a poweramplifier l8, and a radiating antenna system l1, Is. For the purpose ofdeveloping and transmitting a composite synchronizing signal and forsynchronizing the scanning of the video-frequency generator Illtherewith, there is provided apparatus including a line-frequencygenerator 20 and a field-frequency generator 2| having their outputcircuits coupled to a mixing amplifier 22, the output circuit of whichis, in turn, coupled to the videofrequency amplifier |3. Output circuitsof linefrequency generator 20 and field-frequency generator 2| are alsocoupled to the video-frequency signal generator I0. timing-impulsegenerator 23 for the purpose of controlling the operation ofline-frequency generator 20 and field-frequency generator 2|. Thegenerator 23 is preferably stabilized by means of a connection 24 to asuitable source of periodic voltage, for example, to the power-supplycircuit or to the synchronizing-voltage source of motion picturemechanism, where such is employed.

Neglecting for the moment the details of operation of thesignal-translating stage l2, the system just described comprises theelements of a television transmitting system of conventional design and,since the various parts thereof with the exception of stage l2 may be ofany wellknown construction, a detailed description of the general systemand its operation is unnecessary. Briefly, the image of the scene to betransmitted is focused on the target in the signal generator l0 and avideo-frequency voltage is developed thereby in the usual manner and isapplied to the video-frequency amplifier wherein this voltage isamplified and from which it is transmitted through amplifier I2 to thevideo-frequency amplifier l3. The composite synchronizing signaldeveloped by the mixing amplifier 22, as will presently be described inmore detail, is also applied to the video-frequency amplifier L3 inwhich it is mixed with the video-frequency signal and further amplified.The amplified composite signal is supplied to the modulator I wherein itis so impressed upon the carrier wave generated by the oscillator [5 asto develop a modulated-carrier signal. This signal is delivered to thepower amplifier l6 for amplification therein and is thereafter impressedupon the antenna system ll, l8 to be radiated.

Timing pulses developed by the generator 23 are applied to thegenerators 20 and 2| to lock the same in synchronism. An output voltageof each of the generators 20 and 2| is applied to the mixing amplifier22 in order to generate the required composite synchronizing signal fortransmission. Output voltages of generators 20 and 2| are also suppliedto the video-frequency signal generator l0 to synchronize the operationthereof.

Referring now more particularly to the ap- There is also provided a andii. The tube structure is illustrated in more detail in the partiallysectionalized perspective drawing of Fig. 2. The tube is provided withcontrol grids It and 31 which intersect the beams II and II,respectively, the control grids being wide relative to the widths of thebeams in the above-mentioned limited dimension. Conductor II andconductor II are effective individually to couple the grids I! and 31between the input terminals 3|, 8|, effectively to cause the grids tocomprise voltage dividers across the width of the grids. Focusing platesll, 42, maintained near the potential of the cathode 43 of the tube, areprovided for generating the beams 34 and II which are limited to aribbon shape, as described above. The tube is also provided with ananode It, the cathode l3 and the anode It effectively comprisingconcentric cylinders surrounded by the envelope of the tube. In order todeflect the electron beams 34 and 35 in the direction of the limiteddimensions of the beam, that is, circumferentialiy within the tube 32,to control the gain of the stage II; there is provided a suitablebeam-deflecting means, such as a winding ll. surrounding the tube 32andadapted to be excited by direct current from a source it through avoltage divider ll having an adjustable tap ii. The voltage divider BIand the adjustable tap ll therefore are included in a means foradjusting the amount of deflection of the electron beams 34 and 35 toadjust the gain of the stage to any desired value within relatively widelimits by the action of the control grids 38 and 31. The use of such amagnetic beam-deflecting means rather than an electrostatic deflectingmeans facilitates the desired deflection without affecting the meananode current of the tube. A cathode-biasing resistor 52 is provided fortube 32, by-passed for currents of signal condenser I8.

Reference is made to Figs. 3, 4, and 5 for a more detailed descriptionof the construction of the grids of the tube of the signal-translatingstage it. Each of the grids ll and if! is constructed effectively tocomprise a voltage divider coupled between terminals 30, II, asindicated schematically in Fig. 3. where the vertical members 54represent the wires of the grid which are parallel to the cathode 43 ofthe tube. The grid is so constructed as effectively to provide resistors5! coupling adjacent ends of conductors 54, as illustrated in Fig. 3.The control grid therefore effectively comprises across its widthelectron-controlling conductors effectively spaced by resistors. Thegrid may be construct ed, for instance, as illustrated in Fig. 4, wheremica discs 5., it are utilized to support the grid wires 54. Aconductive material, for instance, some sputtered resistive coating ondiscs 56, is utilized effectively to form the resistors 55 of Fig. 3. Amorev complete detail of this construction is illustrated in Fig. 5,wherein the resistive coating is designated by the reference numeral I.

In considering the operation of the signaltranslating stage I! of Fig.1, it will be seen that, due to the voltage-dividing properties of grids3t, 31, substantially the entire signal voltage is available forutilization to control the intensity of beams 34 and 35 when deflectedto the position shown. since the beams intersect the grids near theirhigh signal-potential terminals. Thus, under this condition ofoperation, the siglating stage II effectively has a relafrequency bymeans of a tively high gain. However, if the tap Ii on voltage dividerII is adjusted .to change the current in winding 48, thereby to deflectthe beams 34 and I in a counterclockwise direction, the beams thenintersect portions of the voltage-dividing grids which are at anappreciablylower signal potential. Therefore, under these conditions,the gain of the stage is materially reduced. However. it will be notedthat the unidirectional bias provided for the grids 3t and I! by thecathode resistor 82 is not changed by this adjustment and, inasmuch asthe control grids It and 31 are homogeneous, that is, they have the samespacing for all equivalent circumferential. portions, the direct spacecurrent of the tube does not vary with the gain adjustment. The cathoderesistor 52 therefore is included in the means for uniformly biasing thecontrol grid. 3

Therefore, it is seen that the signal-translating stage I: is oneadapted to have its gain adjusted over a wide range and in which thedirect current component in the signal-output circuit of the stage doesnot vary appreciably with the gain adjustment, thus providing theadvantages mentioned in the preliminary portion of the specification.

Referring now more particularly to Fig. 6 of the drawings, there isillustrated a superheterodyne receiver including a signal-translatingstage in accordance with the invention as the first stage in thesignal-translating channel of the receiver. This receiver comprises,coupled in cascade with an antenna-ground circuit I, H, aradio-frequency amplifier l2 coupled to antenna circuit 6|, I through aselective circuit I1, 63, it, a frequency changer oroscillator-modulator I, an intermediate-frequency amplifier it of one ormore stages, a detector and A. V. 0. supply 61, an audio-frequencyamplifier ll of one or more stages, and a sound reproducer es. Automaticamplification control is secured in a well-known manner by applying aunidirectional voltage derived from A. V. C. supply 61 to the controlelectrodes of one or more of the tubes included in theoscillator-modulator i5 and intermediate-frequency amplifier it.

A novel type of automatic amplification control is also provided withinthe signal-translating stage II, the constructional details of which aregenerally similar to those of stage I! of Fig. 1 and circuit elementswhich are similar in the two figures have identical reference numerals.The signal-translating stage I! differs from that of stage I! of Fig. 1primarily in the means provided for supplying direct current to thewinding 48 to. control the gain of the stage. In the circuit of Fig. 6the voltage provided by the A. V. C. supply 61 is amplified in an A. V.C. amplifier H, the output of which is utilized to provide the directcurrent for winding 48. The general operation of the superheterodynereceiver of this figure is entirely conventional and need not bedescribed in detail.

It is believed that the operation of the signaltranslating stage I! ofFig. 6 will be readily apparent from the description which has beengiven above of the operation of the signal-translating stage it, theonly difference in the operation being that the gain control is effectedin the circuit of Fig. 6 by the direct current supplied by amplifier llrather than by the direct current supplied by the battery 4!. Therefore,the gain of signaltranslating stage I 2' may be varied within very widelimits with substantially no effect upon the source of supply or the,unidirectional operating voltages provided for the tubes of thereceiver.

and modifications as fall within the true spirit,

and scope of the invention.

What is claimed is: r g

1. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and acontrol grid intersecting said-- beam and wide relative to the width ofsaid beam in said limited dimension, means for coupling said gridbetween said input terminals effectively to comprise a voltage divideracross its width, and means for deflecting said electron beam in thedirection 01 its limited dimension to control the gain of said stage bythe action of said control grid.

2. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and ahomogeneou control grid intersecting said beam and widerelative to thewidth of said beam in said limited dimension, means for coupling saidgrid between said input terminals eflectively to comprise a voltagedivider across its width, and means for deflecting said electron beam inthe direction of its limited dimension to control the gain of said stageby the action of said control grid.

3. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and acontrol grid intersecting said beam and wide relative to the width ofsaid beam in said limited dimension, means for coupling said gridbetween said input terminals effectively to comprise a voltage divideracross its width, means for deflecting said electron beam in thedirection of its limited dimension to control the gain of said stage bythe action of said control grid, and means for uniformly biasing saidcontrol grid.

4. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and ahomogeneous control grid intersecting said beam and wide relative to thewidth of said beam in said limited dimension, means for coupling saidgrid between said input terminals effectively to comprise a voltagedivider across its width, means for deflecting said electron beam in thedirection of its limited dimension to control the gain of said stage bythe action of said control grid, and means for uniiormly biasing saidcontrol grid.

5. A signal-translating stage comprising, :a pair the operation of ofsignal-input-terminals, a vacuum tube including means for forming anelectron beam of ribbon shape in said tube whereby the cross-section islimited in one dimension and a control grid been described what are atintersecting said beam and wide relative to the width of said beam insaid limited dimension, means for coupling said grid between said inputterminals eflectively to comprise a voltage divider across its width,and means for deflecting said electron beam in the direction of itslimited dimension to control the gain of said stage by the action ofsaid control grid.

6. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for formin cross-sectionoiwhich limited in at least one dimension and a control grid intersectingsaid beam which is wide relative to the width oi said beam in itslimited dimension and which eilectively comprises across its widthelectron-controlling conductors effectively spaced by resistors, meansfor coupling said grid between said input-terminals efiectively tocomprise a voltage divider across its width, and means for deflectingsaid electron beam in the direction of its limited dimension to controlthe gain of said stage by the action of said control grid.

7. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and acontrol grid intersecting said beam and wide relative to the width orsaid beam in said limited dimension, means for coupling said gridbetween said input terminals eil'ectively to comprise a voltage divideracross its width, and magnetic means for deflecting said electron beamin the direction of its limited dimension to control the gain of saidstage by the action or said control grid.

8. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and acontrol grid intersecting said beam and wide relative to the width ofsaid beam in said limited dimension, means for coupling said gridbetween said input terminals eflectively to comprise a voltage divideracross its width, and a winding surrounding said tube and adapted to beenergized by a unidirectional current for deflecting said electron beamin the direction of its limited dimension to control the gain of saidstage by the action of said control grid.

9. A signal-translating stage comprising, a pair of signal-inputterminals, a vacuum tube including means for forming an electron beamthe cross-section of which is limited in at least one dimension and acontrol grid intersecting said beam and wide relative to the width ofsaid beam in said limited dimension, means for coupling said gridbetween said input terminals eflectively to comprise a voltage divideracross its width, means for deflecting said electron beam in thedirection of its limited dimension, and means for adjusting the amountof deflection to adjust the gain of said stage by the action of saidgrid to any desired value within relatively wide limits.

JOHN C. WILSON.

an electron beam the,

